In order to improve the design of a mobile equipment such as a mobile phone, smartphone and tablet device, application of such a 3D cover glass as illustrated in FIG. 1 to an image display device used in the mobile equipment has been studied. FIG. 1 shows one configuration example of a 3D cover glass 100, whose central part 110 is composed of a flat plane and whose peripheral part is configured of a three-dimensional shaped curved part 120.
The cover glass in the image display device needs to be thinned and is also subjected to a chemical strengthening treatment because it requires a certain strength. In the 3D cover glass having a three-dimensional shaped curved surface in the peripheral part thereof, occurrence of warpage due to the chemical strengthening treatment provides a problem. FIG. 2A and FIG. 2B are schematic views illustrating occurrence of warpage in a 3D cover glass due to the chemical strengthening treatment. Specifically, FIG. 2A is a cross-sectional schematic view illustrating a state before execution of the chemical strengthening treatment, and FIG. 2B is a cross-sectional schematic view illustrating a state after execution of the chemical strengthening treatment, that is, a state of occurrence warpage in a 3D cover glass due to the chemical strengthening treatment. In this case, as illustrated in FIG. 2A, for example, before execution of the chemical strengthening treatment, the central part is flat, whereas, as illustrated in FIG. 2B, after execution of the chemical strengthening treatment, convex warpage occurs in the central part.
Patent Document 1 proposes a method for correcting the warpage of the 3D cover glass due to the chemical strengthening treatment.
Patent Document 1: JP-T 2016-524582